In the performance of density gradient centrifugation, a working fluid is used such as, for example, an aqueous polysaccharide solution commercially available under the trademarks Ficoll-Paque.TM. or Histo-Paque.TM. and having a density larger than that of the liquid phase of the dispersion to be centrifuged and intermediate between the densities of the solid components thereof. Preparatory to centrifugation, the liquid dispersion to be centrifuged is layered on top of a working fluid within a centrifugation vessel with as clean an interface between the two as possible, and upon centrifugation there results a liquid column with a density gradient in which, similar as in column chromatography, each of the solid components of the original dispersion occupies a different layer from where it may be separately recovered.
The crucial problem in the performance of density gradient centrifugation is the charging of the centrifugation vessel so as to ensure a clean interface between the lower body of working fluid and the upper body of liquid dispersion. In accordance with the state of the art various manual techniques and skills have been developed to this end. Thus, by one method the dispersion to be centrifuged, for example native or diluted blood, is first placed into the centrifugation vessel and the heavier working fluid is then carefully pipetted underneath the body of fluid to be centrifuged. Alternatively, the working fluid is first filled into the centrifugation vessel and the liquid to be centrifuged is carefully layered thereon.
Obviously both these procedures are tedious, require a high amount of skill and are unsuitable for serial operation.
U.S. Pat. No. 4,824,560 discloses method and means for centrifugation by which a tubular vessel is used with at least two compartments in a row communicating with one another via a narrow, essentially capillary opening. For operation, the working fluid is charged into the lower compartment and the liquid to be centrifuged into the upper one with no need for any special precautions to avoid mixing prior to centrifugation. While this method has some significant advantage over the above-described purely manual methods, it has the drawback that the rather narrow passage between the compartments provides some resistance even during centrifugation which may prolong the operation. Moreover, the method requires specially devised centrifugation vessels which renders it relatively costly. Furthermore, since in accordance with that method the entire lowermost compartment must be filled with working fluid it is not possible to vary the amount of working fluid in a given centrifugation vessel.
It is the object of the present invention to provide an improved method and means for density gradient centrifugation.